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CONTENTS
Volume 13, Number 6, June 2014
 

Abstract
This study investigated the chloride binding isotherms of various cement types, especially the contributions of C-S-H and AFm hydrates to the chloride binding isotherms were determined. Ordinary Portland cement (OPC), Modified cement (MC), Rapid-hardening Portland cement (RHC) and Low-heat Portland cement (LHC) were used. The total chloride contents and free chloride contents were analyzed by ASTM. The contents of C-S-H, AFm hydrates and Friedel\'s salt were determined by X-ray diffraction Rietveld (XRD Rietveld) analysis. The results showed that OPC had the highest chloride binding capacity, and, LHC had the lowest binding capacity of chloride ions. MC and RHC had very similar capacities to bind chloride ions. Experimental equations which distinguish the chemically bound chloride and physically bound chloride were formulated to determine amounts of the bound chloride basing on chloride binding capacity of hydrates.

Key Words
chloride binding isotherm; C-S-H; AFm; Friedel

Address
Tran Van Mien: Faculty of Civil Engineering, HoChiMinh City University of Technology, HCM City, Vietnam

Toyoharu NAWA: Graduate School of Engineering, Hokkaido University, Sapporo City, Japan

Boonchai Stitmannaithum: Department of Civil Engineering, Chulalongkorn University, Bangkok, Thailand


Abstract
Fibre-reinforced self-compacting concrete (FRSCC) is a high-performance building material that combines positive aspects of fresh properties of self-compacting concrete (SCC) with improved characteristics of hardened concrete as a result of fibre addition. To produce SCC, either the constituent materials or the corresponding mix proportions may notably differ from the conventional concrete (CC). These modifications besides enhance the concrete fresh properties affect the hardened properties of the concrete. Therefore, it is vital to investigate whether all the assumed hypotheses about CC are also valid for SCC structures. In the present paper, the experimental results of short-term flexural load tests on eight reinforced SCC and FRSCC specimens slabs are presented. For this purpose, four SCC mixes – two plain SCC, two steel, two polypropylene, and two hybrid FRSCC slab specimens – are considered in the test program. The tests are conducted to study the development of SCC and FRSCC flexural cracking under increasing short-term loads from first cracking through to flexural failure. The achieved experimental results give the SCC and FRSCC slabs bond shear stresses for short-term crack width calculation. Therefore, the adopted bond shear stress for each mix slab is presented in this study. Crack width, crack patterns, deflections at mid-span, steel strains and concrete surface strains at the steel levels were recorded at each load increment in the post-cracking range.

Key Words
fibre-reinforced self-compacting concrete; self-compacting concrete; crack control; flexural cracking; bond shear stress

Address
Farhad Aslani: Centre for Infrastructure Engineering and Safety, School of Civil and Environmental Engineering, University of New South Wales, Australia

Shami Nejadi: School of Civil and Environmental Engineering, University of Technology Sydney, Australia

Bijan Samali: Institute for Infrastructure Engineering, University of Western Sydney, Australia

Abstract
In this article, by using experimental studies and artificial neural network has been tried to investigate the use of nano-silica as concrete admixture to reduce alkali-silica reaction. If there are reactive aggregates and alkali of cement with enough moisture in concrete, a gel will be formed. Then with high reactivity between alkali of cement and existence of silica in aggregates, this gel will expand by absorption of water, and causes expansive pressure and cracks be formed. At the time passes, this gel will reduce both durability and strength of the concrete. By reducing the size of silicate to nano, specific surface area of particles and number of atoms on the surface will be increased, which causes more pozzolanic activity of them. Nano-silica can react with calcium hydroxide (Ca (OH)2) and produces C-S-H gel. In this study, accelerated mortar bar specimens according to ASTM C 1260 and ASTM C 1567, with different mix proportions were prepared using aggregates of Kerman, such as: none admixture and plasticizer, different proportions of nano-silica separately. BY opening the moulds after 24 hour and curing in water at 80oC for 14 days, length expansion of mortar bars were measured and compared. It was noted that, the lowest length expansion of a specimens shows the best proportion of admixture based on alkali-silica reactivity. Then, prediction of alkali-silica reaction of concrete has been investigated by using artificial neural network. In this study the backpropagation network has been used and compared with different algorithms to train network. Finally, the best amount of nano silica for adding to mix proportion, also the best algorithm and number of neurons in hidden layer of artificial neural network have been offered.

Key Words
Nano-Silica; Alkali-Silica Reaction (ASR); Mix Design; Artificial Neural Network (ANN), Backpropagation

Address
Ramin Tabatabaei, Hamid Reza Sanjari and Mohsen Shamsadini: Department of Civil Engineering, Islamic Azad University, Kerman Branch, Kerman, Iran

Abstract
Structural safety has always been a key preoccupation for engineers responsible for the design of civil engineering projects. One of the mechanisms of structural failure, which has gathered increasing attention over the past few decades, is referred to as \'progressive collapse\' which happens when one or several structural members suddenly fail, whatever the cause (accident, attack, seismic loading(.Any weakness in design or construction of structuralelements can inducethe progressive collapse in structures, during seismic loading. Masonry infill panels have significant influence on structureresponseagainst the lateral load. Therefore in this paper, seismic performance and shear strength of R.C frameswith brick infill panel under various lateral loading patterns are investigated. This evaluation is performed by nonlinear static analysis. The results provided important information for additional design guidance on seismic safety of RC frames with brick infill panel under progressive collapse.

Key Words
progressive collapse;brick infill panel;Lateral loading;seismic performance; shear strength

Address
HamidrezaTavakoli: Assistant Professor of Civil Engineering, BabolNoshirvani University of Technology, Iran

Soodeh Akbarpoor: Structure Engineering, Mazandaran University of Science& Technology, Iran

Abstract
Many building codes use the empirical equation to determine fundamental period of vibration where in effect of length, width and the stiffness of the building is not explicitly accounted for. In the present study, ANN models are developed in three categories, varying the number of input parameters in each category. Input parameters are chosen to represent mass, stiffness and geometry of the buildings indirectly. Total numbers of 206 buildings are analyzed out of which, data set of 142 buildings is used to develop these models. It is demonstrated through developed ANN models that geometry of the building and the sizes of the columns are significant parameters in the dynamic analysis of building frames. The testing dataset of these three models is used to obtain the empirical relationship between the height of the building and fundamental period of vibration and compared with the similar equations proposed by other researchers. Experiments are conducted on Mild Steel frames using uniaxial shake table. It is seen that the values obtained through the ANN models are close to the experimental values. The validity of ANN technique is verified by experimental values.

Key Words
dynamic analysis; artificial neural network; data driven tools

Address
Shardul G. Joshi and Shreenivas N. Londhe: Department of Civil Engineering, Vishwakarma Institute of Information Technology, Pune. MH 411048. India

Naveen Kwatra: Department of Civil Engineering, Thapar University, Patiala, Punjab, 147004. India

Abstract
Estimating the workability of self-compacting concrete (SCC) is very important both in laboratories and on construction site. A method using visual information during the mixing process was proposed in this paper to estimate the workability of SCC. First, fourteen specimens of concrete were produced by a single-shaft mixer. A digital camera was used to record all the mixing processes. Second, employing the digital image processing, the visual information from mixing process images was extracted. The concrete pushed by the rotating blades forms two boundaries in the images. The shape of the upper boundary and the vertical distance between the upper and lower boundaries were used as two visual features. Thirdly, slump flow test and V-funnel test were carried out to estimate the workability of each SCC. Finally, the vertical distance between the upper and lower boundaries andthe shape of the upper boundary were used as indicators to estimate the workability of SCC. The vertical distance between the upper and lower boundaries was related to the slump flow, the shape of the upper boundary was related to the V-funnel flow time. Based on these relationships, the workability of SCC could be estimated using the mixing process images. This estimating method was verified by three more experiments. The experimental results indicate that the proposed method could be used to automatically estimate SCC workability.

Key Words
self-compacting concrete; workability; mixing process; digital image processing; slump flow test; V-funnel test

Address
Shuyang Li and Xuehui An: State Key Laboratory of Hydro Science and Engineering, Tsinghua University, 100084-Beijing, China

Abstract
In this paper, a theoretical and experimental study of the sectional behaviour of reinforced concrete beams subjected to short-term loads is carried out. The pure bending behaviour is analysed with moment-curvature diagrams. Thus, the experimental results obtained from 24 beams tested by the authors and reported in literature are compared with theoretical results obtained from a layered model, which combines the material parameters defined in Model Code 2010 with some of the most recognized tension-stiffening models. Although the tests were carried out for short-term loads, the analysis demonstrates that rheological effects can be important and must be accounted to understand the experimental results. Another important conclusion for the beams tested in this work is that the method proposed by EC-2 tends to underestimate the tension-stiffening effects, leading to inaccuracies in the estimations of deflections. Thus, the actual formulation is analysed and a simple modification is proposed. The idea is the separation of the deflection prediction in two parts: one for short-term loads and other for rheological effects (shrinkage). The results obtained are in fairly good agreement with the experimental results, showing the feasibility of the proposed modification.

Key Words
reinforced concrete; moment-curvature; tension stiffening; beam growth; serviceability; shrinkage; eurocode 2; Model Code 2010; effective modulus of inertia

Address
Javier Ezeberry Parrotta, Hugo Corres Peiretti and Alejandro Pérez Caldentey: Polytechnic University of Madrid. Profesor Aranguren 3, 28040 Madrid, Spain

Viktor Gribniak: Vilnius Gediminas Technical University. Sauletekio av. 11, 10223 Vilnius, Lithuania and Institute of Polymer Mechanics, University of Latvia. Raina Blvd. 19, 1586 Riga, Latvia



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